The development of a non-invasive means of measuring oxygen saturation in the fundus of the human eye would be useful in the diagnosis and monitoring of numerous disorders, including diabetic retinopathy, arterial venous occlusion disease, and glaucoma. In these studies, a practical system to evaluate oxygen saturation in the retina and optic nerve head using a recent innovation, hyperspectral imaging, will be developed. The hyperspectral technique measures spectral changes within the visible and infrared spectra and provides information on the molecular state of hemoglobin. The hyperspectral imaging device will allow measurement - non-invasively and in real time - of reduction and/or elevation in tissue oxygenation. The distinct optical signature of biological materials such as oxy-hemoglobin and deoxy-hemoglobin as a function of their reflectance spectra will enable determination of their relative concentrations. In recent years, reflectance oximetry has been developed for the non-invasive measurement of oxygen saturation changes in the vessels of the fundus using double, triple, and multiple wavelength reflectance imaging. The hyperspectral reflectance oximetry that will be employed in these studies will permit the first non-invasive measurement for oxygen saturation in the optic nerve head tissue, and the hyperpectral data to be collected will intrinsically include all of the multiple wavelength spectra obtained in earlier approaches. The new system will be tested in two specific aims: 1) hyperspectral imaging will be used to non-invasively evaluate the stimulus-response relationship between perturbations in intraocular pressure (lOP) (10-50 mm Hg) and oxygen saturation in optic nerve head tissues and in retinal artery/vein pairs for a graded series of hypoxic states, and 2) the same studies will be performed in eyes with early stage experimental glaucoma. With this new approach, it will be possible to determine how acute changes in lOP alone or in combination with chronic lOP elevation (glaucoma) affect the three distinct microcirculations of the optic nerve head (surface nerve fiber layer; prelaminar region; lamina cribrosa) independently and/or collectively. The proposed studies are motivated by the potential for clinical application of this innovative technology in the early diagnosis of and monitoring of therapy for ocular vascular diseases in which the associated hypoxia may eventually lead to loss of vision.